1. Technical Field of the Invention
This invention relates to a belt driven bicycle, and more particularly to an apparatus for driving such a belt.
2. Prior Art
FIG. 7 shows a conventional belt driving apparatus for a bicycle. More specifically, this belt driving apparatus comprises a driving pulley 2 of large diameter mounted on a crank shaft 1 and a driven pulley 3 of small diameter mounted on a shaft on the side of a rear wheel (not shown) with a toothed belt 4 being trained over the driving and driven pulleys 2, 3. In the belt driving apparatus fabricated as above-mentioned idlers 5a, 5a which are close to each other urge the toothed belt 4 such as to apply a certain tensile force thereto in order to prevent the toothed belt 4 from being removed or slipping. When toothed belt 4, if urged by the idlers 5a, 5a is rotated and driven while being in a curved condition in the position where the idler 5a is located, the belt 4 becomes greatly damaged. This requires the belt to be replaced after a short time.
FIG. 8 shows another conventional belt driving apparatus which comprises a driving gear 6 mounted on the crank shaft 1, a floating wheel 7 with internal teeth 7a which meshes with the driving gear 6, and a toothed belt 4 trained over the floating wheel 7 for rotatably driving the driven pulley 3. The belt driving apparatus arranged as aforementioned is required to secure the rotational speed of the driven pulley 3 by use of the driving gear 6 and a floating wheel 7, each of large diameter, since the floating wheel 7 is reducedly driven by the driving gear 6. The disadvantage derived from the use of the driving gear 6 and the floating wheel 7 of large diameter is that the weight of the bicycle is increased. In a belt driving apparatus of this type, the internal teeth 7a in a position adjacent a point A of the floating wheel 7 is disengaged from the teeth of the driving gear 6 or goes out of mesh therewith due to the inconsistent extent of eccentricity of the floating wheel 7 when the pedals are worked energetically. This may possibly cause damage to the teeth.
An alternative belt driving apparatus has been proposed wherein a driving gear of small diameter is disposed in a drum with internal teeth mounted on a crank shaft such that they mesh with each other, thereby obtaining a higher rotational speed. However, a large difference in diameter between the drum and the driving gear involves a disadvantage in that noise is readily produced when the internal teeth of the drum mesh with the driving gear.